From: Tejun Heo <tj@kernel.org>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
Linux PM list <linux-pm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
horms@verge.net.au, "pavel@ucw.cz" <pavel@ucw.cz>,
Len Brown <lenb@kernel.org>
Subject: Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system_sleep()
Date: Wed, 18 Jan 2012 09:30:37 -0800 [thread overview]
Message-ID: <20120118173037.GE30664@google.com> (raw)
In-Reply-To: <4F16FF0D.1030606@linux.vnet.ibm.com>
Hello, Srivatsa.
On Wed, Jan 18, 2012 at 10:49:09PM +0530, Srivatsa S. Bhat wrote:
> I agree, but I was trying to keep the comment from growing too long ;)
It doesn't have to be long. It just has to give some meaning to the
decision. AFAICS, it is correct to call try_to_freeze() on
unlock_system_sleep() regardless of 20sec window. There's no
guarantee the unlocking task is gonna hit try_to_freeze() elsewhere
and not calling it actually makes the interface buggy.
That said, it causes a problem because unlock_system_sleep() is called
in a special context during later stage of hibernation where the usual
expectation - that a freezable task which sees a freezing condition
should freeze - doesn't hold.
The correct solution would be somehow marking that condition so that
either try_to_freeze() doesn't get invoked or gets nullified -
e.g. making the SKIP thing a counter and ensure the hibernating task
has it elevated throughout the whole process. Alternatively, if the
code path is limited enough, using a different version of the unlock
function, unlock_system_sleep_nofreeze() or whatever, would work too -
this is a popular approach for synchronization functions which
interacts with scheduler and preemption.
For now, as a quick fix, maybe not calling try_to_freeze()
unconditionally is okay, I don't know, but it's a hack.
Thanks.
--
tejun
next prev parent reply other threads:[~2012-01-18 17:30 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-17 22:45 [PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system_sleep() Rafael J. Wysocki
2012-01-17 23:15 ` [Update][PATCH] " Rafael J. Wysocki
2012-01-18 12:59 ` Srivatsa S. Bhat
2012-01-18 15:42 ` Tejun Heo
2012-01-18 16:54 ` Srivatsa S. Bhat
2012-01-18 16:58 ` Tejun Heo
2012-01-18 17:19 ` Srivatsa S. Bhat
2012-01-18 17:30 ` Tejun Heo [this message]
2012-01-18 17:33 ` Tejun Heo
2012-01-19 10:37 ` Pavel Machek
2012-01-19 10:55 ` Srivatsa S. Bhat
2012-01-19 17:40 ` Pavel Machek
2012-01-19 18:10 ` Srivatsa S. Bhat
2012-01-18 19:22 ` Srivatsa S. Bhat
2012-01-18 19:30 ` Tejun Heo
2012-01-18 19:46 ` Srivatsa S. Bhat
2012-01-18 20:29 ` Srivatsa S. Bhat
2012-01-18 22:04 ` Tejun Heo
2012-01-18 22:22 ` Rafael J. Wysocki
2012-01-19 14:40 ` Srivatsa S. Bhat
2012-01-19 22:35 ` Rafael J. Wysocki
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